This application relates to well tools and more particularly to centralizers and/or scrapers for pump rod strings.
The usual apparatus for pumping well fluids from a well to the surface, through a tubing which extends from the surface to below a fluid producing formation penetrated by the well, includes a pump connected to the lower end of the tubing which has a plunger or "traveling valve" which is reciprocated in the longitudinal barrel of the pump by a string of pump rods, the bottom rod being connected to the traveling valve, the top rod of the rod string being connected to a motor driven means for alternately pulling the string upwardly and then allowing the string to be moved downwardly by gravity.
Since the weight of the tubing string, of the pump rod string provides the force necessary to cause well fluids to flow upwardly through the tubing, if the resistance to the downward movement of string of tubing by the upwardly flowing well fluids, especially past such obstructions to fluid flow as centralizers or scrapers mounted on the rods, the rod string will move downwardly relatively slowly thus reducing the rate of production of the well fluids. The centralizers decrease the flow space area between the centralizers, the rod and the tubing. In addition, if the pump and lower end portions of the rod string offer a relatively great resistance to downward movement of the rod string, the weight of upper portions of the rod string may cause lower portions of the rod string to be placed under great compression loads which tend to cause such lower portions to bend and buckle and their centralizers to be moved with great force against the internal surfaces of the tubing.
In addition, the bottom end portion of the rod string must be held in concentric longitudinal alignment with the pump plunger both to minimize wear of the pump lunger and barrel and to decrease the resistance to downward movement of the plunger in the barrel.